Torque converters are often provided with a lockup device for transmitting torque directly from the front cover to the turbine. This lockup device has a piston that can frictionally couple to the front cover, a drive plate onto which the piston is fixed, a plurality of torsion springs supported by the drive plate, and a driven plate elastically coupled to the piston in a rotational direction by the torsion springs. The driven plate is fixed to the turbine.
The piston divides a space between the front cover and the turbine in an axial direction and can be moved in the axial direction by a hydraulic pressure difference in both axial-direction sides. Also, torque of the front cover is transmitted to the lockup device when an annular friction facing provided on an outer peripheral portion of the piston is pressed against a flat friction surface of the front cover.
When torque is being transmitted with the lockup device, it is necessary to change the torsion springs to a lower stiffness and a wider twisting angle in order to absorb and attenuate torque fluctuations inputted from an engine. Therefore, as shown in Patent Document 1, a device has already been proposed in which torsion springs are arranged on each of an outer peripheral portion and an inner peripheral portion. The torsion springs on the outer peripheral side and the torsion springs on the inner peripheral side are coupled by an intermediate member.
Laid-open Japanese Patent Application Publication No. 2001-82577 (Patent Document 1) is an example of the related art